The major emphasis in early research on implants was performed within the field of orthopedics. (Bechtol, C. D., Ferguson, Jr., A. B., and Laing, P. G. Metals and Engineering in Bone and Joint Surgery. Williams and Wilkins Co., Balt. Chapter 1, 1-18 (1959); Scales, J. T. Arthroplasty of the Hip Using Foreign Materials: A History, Paper 13, A Symposium, Institute of Mechanical Engineers, Vol. 181 Part 3J, 63-84, (1967); Weisman, S. Metals for Implantation in the Human Body. Ann. N.Y. Acad. Sci. 146, 80-95, (1968)). The most significant addition to implant surgery in the last twenty years has been the development of prostheses for vascular and cardiac reconstruction (Wesolowski, S. A., Martinez, A., and McMahone, J. D. The Use of Artificial Materials in Surgery, "Current Problems in Surgery." Year Book Medical Publishers, Inc., Chicago (1966). A major problem involved in the use of prosthetic alloplastic materials has been severe occlusive thrombogenicity (Hufnagel, C. A. The Use of Rigid and Flexible Plastic Prostheses for Arterial Replacement, Surgery, 37:165, (1955)). The search for acceptable materials and designs for vascular prostheses was of great importance because of a number of problems which were encountered with the use of polymeric and metal prostheses, autologous, homologous and heterologous bypass grafts in man. (Johnson, W. D. Auer, J. E. and Tector, A. T., Late Changes in Coronary Vein Grafts Am. Jour. of Cardiol. 26:640, (1970). and Artegraft Conference, Johnson and Johnson, Toronto, Ontario, Canada. June 23, (1973)).
Following the development of open heart surgery, an enormous effort was made in the field of prosthetic heart valves. The first successful development in this area was made by Goodman, Berg and Stuckey (Wesolowski, S. A. et al The Use of Artificial Materials in Surgery, "Current Problems in Surgery" Year Book Medical Publishers, Inc., Chicago (1966)). They produced the first completely thromboresistant prosthetic heart valve. This valve was later improved by Dr. Albert Star and Edwards Laboratories (Edwards, W. S. and Smith, L. Aortial Valve Replacement with a Sub Coronary Ball Valve. Sur. Forum 9:309 (1958); Starr, A. Mitral Valve Replacement with a Ball Valve Prosthesis. British Heart Journal, 33 Supp. 47 (1971). A number of valves were further developed by several corporations. These included the Bjork-Shiley valve which is the most successful of the prosthetic heart valves available today. More recently, glutaraldehyde tanned porcine collagen prosthetic heart valves developed by the Hancock Laboratory (Sauvage, L. R., Wesolowski, A. S., Sawyer, P. N. et al. Prosthetic Valve Replacement Ann. of the N.Y. Academy of Sci. 146:289 (1968 )) have proven useful. They are resistant to intravascular thrombosis and have maintained their tensile strength following several years of implantation in man. Thus, a host of glutaraldehyde tanned collagen valvular prostheses have proven useful in man with respect to long term function and resistance to thrombosis.
Early attempts to replace blood vessels in man involved the use of rigid tubes of gold, silver, aluminum, magnesium, as well as the later development of polyethylene and polymethyl acrylic tubes (Szilagyi, D. E. Long Term Evaluation of Plastic Arterial Substitutes: An Experimental Study, Surg. 55:165 (1964); Woodward, S. C. Biological End Points for Compatibility, Plastics in Surgical Implants ASTM-STP 386, A Symposium on Surg. Implants, Indianapolis, Indiana (1964); Sawyer, P. N. Wu, K. T., Wesolowski, A. S., Brattain, W. H. and Boddy, P. J. Long Term Patency of Solid Wall Vascular Prostheses, Arch. Surg. 91:735, (1965)). In the majority of cases, these prostheses did not function satisfactorily. A major breakthrough came in 1952 when Voorhees and Blakemore described their experiments with a cloth prosthesis of Vinyon. (Voorhees, A. B., Jr., Jaretski, 111, A. and Blakemore, A. H. Use of tubes constructed from Vinyon-"N" Cloth in bridging Arterial Defects. Ann. Surg. 135;332 (1952)). This material was easy to handle, preclottable and resistant to thrombosis following implantation, although tensile strength, in situ, was lost with the passage of time. Preclotting the graft with the patient's blood produced a compound prosthesis, whereby, the lumen was covered by a fibrous neo-intima and the adventitia was enclosed by a fibrous capsule, which resulted in a well tolerated graft. Presently, the Decron graft is considered to be the most successful cloth type graft. (Sawyer, P. N. et al. Vascular Graft Symposium, Current Status and Future Trends. NIH (1976)).
Early attempts at vessel substitution with materials of biologic origin were carried out using arteries from cadavers (Wesolowski, S. A. and Sauvage, L. R. Heterologus Aortic Hetergrafts with Special Reference to Recipient Site, Ethylene Oxide Freeze Dry Preparation and Specied of Origin, Ann. Surg. 145:187 (1957). On the whole, these homografts functioned well for a period of time, but were soon replaced by fibrous tissue and calcium salts. This resulted in an inelastic structure, susceptible to thrombus, fracture, and aneurysm formation (Sauvage, L. R. and Wesolowski, A. S. Healing and Fate of Arterial Grafts, Surg. 38:1090 (1955)).
Following failure of the homografts, autografts from a patient's veins (saphenous) were used. Currently, the implantation statistics show that the saphenous vein is superior to synthetic implants (Sawyer, P. N. et al, Vascular Graft Symposium, Sauvage, L. R. and Wesolowski, A. S. Healing and Fate of Arterial Grafts, supra, and Vlodaver, C. and Edwards, J. E. Pathological Changes in Aortocoronary Arterial Saphenous Vein Grafts. Circulation 44:719 (1971)). When the saphenous vein is not available, i.e., the question arises as to which implant should be used. Experience has shown that a vascular graft must: (i) have an appropriate porosity (10,000-20,000 ml of water/square cm/minute) (Sawyer, P. N., Wu, K. T., Wesolowski, S. A. Brattain, W. H. and Boddy, P. J. An Aid in the Selection of Vascular Prosthesis. Proc. Natl. Acad. Sci., U.S.A., 53:1965.), (ii) be blood compatible, (iii) possess tensile strength and (iv) be easy to handle with respect to sewing characteristics (Sawyer, P. N. and Srinivasan, S. New Approaches in the Selections of Materials Compatible with Blood. Artificial Heart Prog Conf Proc Chapter 22, 1969).
In a effort to overcome the problems of porosity, junctional thrombosis, and small diameter compliance exhibited by most implants in the periphery, I have conducted research on copolymeric collagen remnants from bovine carotid and brachial arteries. The collagen remains intact following enzymatic digestion (ficin) and is then glutaraldehyde tanned and negatively charged.
When implanted, these grafts reveal a striking tendency to remain thromboresistant and maintain their tensile strength as opposed to other commercially available collagen grafts that possess a limited degree of patency with early loss of tensile strength. My copolymeric grafts have remained patent in the femoral-popliteal, carotid and coronary positions (Vascular Graft Symposium, supra).
As to way these types of grafts perform so well, conclusive answers are not yet available. Scanning electron microscopic studies indicate that when the grafts fail, they become occluded by an atypical thrombus. It is therefore obvious that the success of this type of graft depends upon (i) the surface modification characteristics of the collagen (ii) blood interfacial reactions' occurring, (iii) structural aspects of the collagen surface.